Estrogen Antagonists

Question 1

Tamoxifen

Answer 1

Class: Non-steroidal anti estrogen, SERM

Mechanism of action: Blocks estrogen from binding ER

Therapeutic uses: ER positive BC

Toxicities: Pro-estrogen effect in bone and endometrium

Other: weak affinity and therefore must be used at very high doses

Question 2

Clomiphene citrate

Answer 2

Class: Non-steroidal anti-estrogen

Mechanism of action: Prevents estrogen binding in the hypothalamus eliminating negative feedback and increased secretion of gonadotropins and LH causing ovulation

Therapeutic uses: Stimulate ovulation

Toxicities: Hot flashes, multiple pregnancies, stomachache, headache, upset stomach,

Other: cis is a weak estrogen agonist while trans is a strong estrogen antagonist.